This proposal has the aim of contributing to our understanding of how cells control the expression of their different collagen genes. Such a study on collagen genes is particularly important because of the extraordinary ubiquity and importance of collagen in vertebrate organisms. Each vertebrate cell carries the gene for at least 5 distinct collagen chains, yet expresses only a particular subset of these at any one developmental stage. Some promising cell-culture systems for the study of the control of these genes are available. The approach being taken is to isolate collagen mRNAs of sufficient purity to be used as templates for synthesis of complementary DNAs (cDNAs). Current work focuses on obtaining and cloning the cDNA from Type II collagen mRNA. This cloned cDNA will then be used to screen a phage library of cloned chicken genomic DNA so that the structure of the Type II gene can be analyzed. A second current objective is to use cloned Type I and II cDNAs to measure the concentrations of the corresponding mRNAs in cultures of chick cartilage cells that are undergoing a change in gene expression from Type II to Type I collagen.